Location System

1. A system comprising a primary terminal and a plurality of secondary terminals, wherein the primary terminal is configured to determine location data for the primary terminal by performing simultaneous localization and mapping, SLAM, and to send signals that are received by any of the plurality of secondary terminals when in range of the primary terminal, wherein at least a secondary terminal of the plurality of secondary terminals is configured to send a confirmation message to the primary terminal when it receives at least a signal of the signals from the primary terminal, the confirmation message comprising a secondary terminal identifier, and wherein the primary terminal is configured to send a location reporting message to a location processing server, the location reporting message comprising data relating to the location data and data relating to the confirmation message sent by the secondary terminal.

2. The system according to claim 1 , wherein the signals comprise the location data for the primary terminal.

3. The system of claim 1 , wherein the signals comprise proximity-limited communication signals.

4. The system of claim 1 , wherein the location reporting message sent to the location processing server comprises one or more secondary terminal identifiers received by the primary terminal.

5. The system of claim 1 , wherein at least a further secondary terminal of the plurality of secondary terminals is configured to determine a location of the further secondary terminal in accordance with the signal received from the primary terminal.

6. The system of claim 5 , wherein the further secondary terminal is configured to send a further location reporting message to the location processing server, the further location reporting message comprising the location of the further secondary terminal.

7. A primary terminal comprising an imaging sensor, a processor, and a memory, the memory storing facility map data for a facility, the primary terminal being configured to: compare data received from the imaging sensor with the facility map data; determine location data for the primary terminal within the facility in accordance with the comparison; send a signal; receive one or more confirmation messages from one or more of a plurality of secondary terminals, the or each confirmation message being sent in response to receiving the signal.

8. The primary terminal according to claim 7 , wherein the signal includes the location data.

9. The primary terminal of claim 7 , wherein the primary terminal is further configured to send a location reporting message to a location processing server, the location reporting message comprising the location data and data relating to the one or more confirmation messages received from one or more of the plurality of secondary terminals.

10. The primary terminal of claim 9 , wherein the primary terminal is further configured to send a location reporting message to the location processing server if no confirmation messages are received from the plurality of secondary terminals within a reporting period, the location reporting message sent to the location processing server comprising the location data.

11. A method of determining a location of secondary terminals within a facility, the method comprising: a) one or more of a plurality of primary terminals determining location data for the one or more of the plurality of primary terminals, respectively, by performing simultaneous localization and mapping, SLAM, and sending signals to one or more of a plurality of secondary terminals; and b) determining the location of the one or more secondary terminals in accordance with one or more of the signals received by the one or more secondary terminals from the one or more of the plurality of primary terminals.

12. The method of claim 11 , wherein in step b) the one or more secondary terminals which receive the one or more of the signals send one or more confirmation messages to a respective primary terminal of the one or more of the plurality of primary terminals, the one or more confirmation messages comprising a secondary terminal identifier.

13. The method of claim 12 , the method further comprising the one or more of the plurality of primary terminals sending location reporting messages to a location processing server, the location reporting messages comprising the location data for the one or more of the plurality of primary terminals and data relating to the one or more confirmation messages received by the respective primary terminal.

14. The method of claim 13 , wherein the location reporting messages sent to the location processing server comprise each of one or more secondary terminal identifiers received by the respective primary terminal.

15. The method of claim 11 , the method further comprising a secondary terminal of the one or more secondary terminals determining its location in accordance with the signals received from the one or more of the plurality of primary terminals.

16. The method of claim 15 , the method further comprising the secondary terminal sending a message to a location processing server, the message comprising the location of the secondary terminal.